Smoke Movement and Control

Much of the research in this area involves estimating the amount of smoke production. Such an estimate is a prerequisite to determining exhaust capacities of venting systems in large spaces such as atria and arenas. A recent study was conducted to assess the impact of increased make-up air velocity on smoke production. The current restriction defined in the design standard, by NFPA 92 states "The makeup air velocity shall not exceed 200 ft/min (1.02 m/sec) where the makeup air could come into contact with the plume unless a higher makeup air velocity is supported by engineering analysis." This limitation not only limits creative and aesthetic atria designs but may also represent a significant cost. The recent study used a CFD model (Fire Dynamics Simulator) to analyze the effect of make-up air injected by a variety of vent sizes at elevations at or below the top of the flames. The study focused on identifying worst-case scenarios for the interaction of make-up air with an axisymmetric plume, by applying computer modeling to simulate multiple configurations, observe the results, and adapt further simulations to elicit the most extreme cases. A mass flow rate diagnostic, related to the increase in entrainment, i.e. smoke production, was developed to assess the increase in the rate of smoke production with a specified make-up air velocity with that produced with no mechanical make-up air. The most significant smoke production increase and smoke layer stabilization descent was associated with a 1 MW fire, with lesser increases observed for 2.5 MW and 5 MW fires. Also, as the make-up air is introduced further from the edge of the flame, the effect of the airflow velocity is reduced.

Additional research has been conducted on stairwell pressurization systems using the software CONTAM. The research sought to evaluate the effect of building leakage rates and outdoor temperature on fan capacities needed to adequately pressurize the stairwell.